SEMINAR INFORMATION

Title: Transport dynamics and transport-coupled reaction kinetics in complex media: ligand-passivated nanoparticles in hydrophobic nanoconfinement

Speaker : Prof. Ji-Hyun Kim (Chung-Ang University)

Thermal motion of molecules and ensuing reaction process occur ubiquitously across various systems. In particular, much attention has been devoted to studying transport dynamics in complex fluids, but a quantitative understanding of both transport and transport-coupled reaction processes in complex disordered environment within a unified framework remains elusive, primarily due to the lack of not only the appropriate analytical tools to investigate the dynamics of individual particles at microscopic scales but of the relevant experimental data to validate the tools. Here, we directly monitor the stochastic thermal motion and coalescence dynamics of gold nanoparticles smaller than 5 nm, using graphene liquid cell (GLC) transmission electron microscopy. We also present a novel model of transport dynamics and transport-coupled reaction kinetics in disordered environment, providing a unified, quantitative explanation of our experimental observations. The nanoparticles in a GLC exhibit non-Gaussian, diffusive motion, signifying dynamic fluctuation of the diffusion coefficient due to the dynamically heterogeneous environment surrounding nanoparticles, including organic ligands on the nanoparticle surface. Our study also shows that the dynamics of nanoparticle coalescence is controlled by two elementary processes: diffusion-limited encounter-complex formation and the subsequent coalescence of the encounter complex through rotational motion, where surface-passivating ligands play a crucial role. In addition to nanoscience, this work provides a new perspective in understanding various biological processes in living cells.